460 MPa class hot-rolled steel strip for building structures resistant to corrosion in areas with ocean wave spray, and method for manufacturing the same.

Abstract

This disclosure relates to hot-rolled steel strips for building structures and a method for manufacturing the same. The hot-rolled steel strips include a base layer, a corrosion-resistant layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer. The base layer contains the following chemical elements by mass percent: C: 0.03-0.13%, Si: 0.15-0.35%, Mn: 1.00-1.50%, P: 0.0005-0.003%, S: 0.0005-0.01%, Cr: 0.10-0.65%, Ni: 0.2-1.0%, Cu: 0.10-0.25%, Al: 0.020-0.050%, Ti: 0.0090-0.0160%, Nb: 0.060-0.100%, N: 0.0005-0.0050%, V: 0.08-0.25%, with the remainder being Fe and other unavoidable impurities. The corrosion-resistant layer is made from industrial-grade pure titanium. The base layer of the hot-rolled steel strip for building structures according to this disclosure has a yield strength of ≥460 MPa, a tensile strength of ≥580 MPa, a yield ratio of ≤0.81, and an impact energy of ≥190 J at -40°C; the corrosion rate of the corrosion-resistant layer against ocean wave spray is ≤0.006 mm / year; and the interfacial transition layer has a thickness of ≤8 μm and an interfacial shear strength of ≥268 MPa.

Description

Technical Field

[0001] Technical Field The present disclosure relates to steel for building structures and a method for manufacturing the same, and more particularly to hot-rolled strip steel for building structures having corrosion resistance in the splash zone of sea waves and a method for manufacturing the same.

Background Art

[0002] Background Art The marine environment is an extremely harsh and complex corrosion environment. Seawater is a strong electrolyte solution with a high chloride ion concentration. Steel facilities, as the main structures of marine engineering facilities, are extremely prone to electrochemical reactions with the surrounding media and suffer severe corrosion, significantly shortening the service life of these facilities. Especially in the splash zone of sea waves of facilities (the most severe corrosion zone in the marine environment), various facilities are affected by a series of external factors such as wet-dry cycles, sea spray, sunlight, corrosive components in the atmosphere, and oxygen, and the corrosion of materials becomes particularly serious.

[0003] According to investigations, the splash zone of steel piles in facilities such as port terminals and offshore oil platforms generally suffers corrosion that is 3 to 10 times more severe than that in fully submerged sea areas. When serious local corrosion damage occurs to the steel piles, the supporting force of the entire facility is significantly reduced, the service life is shortened, which may even lead to a situation where production safety is impaired and the facility is prematurely discarded.

[0004] In the splash zone of sea waves, it is located in the wet-dry circulation zone and has abundant oxygen supply, so the generated corrosion products have no protective effect; due to the scattering of seawater, sea spray directly hits the metal surface, causing serious corrosion. According to corrosion test and investigation results, under normal environments, the average corrosion rate of ordinary carbon steel, low alloy steel, etc. in the marine atmosphere is about 0.03 - 0.08 mm / year, while in the splash zone of sea waves, it is 0.3 - 0.5 mm / year. In the splash zone of sea waves, steel piles are easily subject to serious corrosion damage, which significantly reduces the supporting force of the entire steel structure, affects safe production, shortens the service life, and leads to premature abandonment.

[0005] Based on the above operating conditions, industrial-grade pure titanium is selected as the corrosion-resistant layer. Titanium is highly chemically reactive and readily reacts with oxygen in the air to form oxides. The oxides on the surface of titanium metal are dense and stable and possess strong "self-healing" capabilities. The "self-healing" capability of titanium oxide mainly refers to the fact that if the titanium oxide film is damaged somewhere on the surface of the titanium material, a new layer of titanium oxide film is quickly formed, preventing further contact of corrosive media with the titanium.

[0006] Steel used in offshore structures must not only meet corrosion resistance requirements but also exhibit good mechanical properties. Among these, yield ratio and low-temperature impact toughness are increasingly important indicators for structural steel. The yield ratio is the ratio of the yield strength to the tensile strength of steel, and its magnitude reflects the steel's ability to avoid stress concentration during plastic deformation. The lower the yield ratio, the more evenly the plastic deformation of the steel can be distributed over a wider area. Under the action of seismic forces, the plastic deformation of a steel structure system composed of steel with a low yield ratio is evenly distributed over a wide area; on the other hand, in materials with a high-strength yield ratio, strain concentration can occur, reducing the overall plastic deformation capacity of the steel, which can lead to brittle fracture of the structure, causing instability and sudden collapse.

[0007] Steel undergoes a brittle transition in low-temperature environments, changing its fracture mode from ductile fracture to brittle fracture. Its engineering significance lies in the fact that, when steel operates above this temperature, structures will not undergo brittle fracture. Therefore, for steel used in structures, it is usually necessary to impose appropriate requirements on its low-temperature impact properties depending on the environment in which the material is used. Ocean temperatures vary significantly at different latitudes. For example, near the Bohai Sea in China, coastal water temperatures can reach below -20°C in winter. For this reason, building materials need to have good impact properties at -40°C to avoid brittle fracture.

[0008] However, when improving the plasticity and toughness of steel, if the increase in tensile strength is small, the yield ratio will rise significantly, making it difficult to maintain a low yield ratio.

[0009] Chinese patent application CN201210260231.7 discloses a method for manufacturing a titanium-steel-titanium double-sided clad plate, the method comprising: stacking four titanium plates and three steel plates in a specific order within a closed frame welded together by the two outermost steel plates; adding a separating agent prepared by mixing 1 part by weight of activated α-Al2O3 and 1.5 parts by weight of a 4% polyvinyl alcohol aqueous solution between the titanium plates; and using a nickel-based alloy as a transition layer between the titanium plates and steel plates. It is heated to 500-630°C and vacuum-treated at a vacuum of 20-200 Pa for 1-2 hours. It is characterized by performing welding after slab assembly but before vacuum treatment, and the welding process can be done using ordinary arc welding and submerging. Compared to welding under vacuum conditions, the welding requirements are lower, the cost is lower, and there is no need to construct a separate vacuum chamber. Subsequently, the clad slab is subjected to a conventional heating furnace and rolled at a rolling temperature of 700-900°C to achieve cladding. By sealing and welding the outermost steel plate and then vacuum-treating it, carbon in the gas is separated, and a nickel-based alloy separation layer is applied between them to prevent TiC formation at the interface. As a result, a titanium-steel clad plate with a shear strength of 230-260 MPa and an interfacial bonding rate of 99.6-100% is obtained.

[0010] Chinese patent application CN201710769999.X discloses a method for manufacturing titanium-steel clad sheets. The method includes: selecting surfaces in a titanium-steel clad slab that will come into contact with each other, applying a highly heat-resistant, carbide-resistant, and nitridation-resistant separation coating to the contacting titanium surfaces, and drying at room temperature. After drying is complete, the titanium slabs are aligned and stacked in pairs, with a steel slab sandwiched between them to complete the assembly and obtain a clad slab. The thickness of the titanium sheets used is greater than 2 mm, and the thickness of the steel sheets is greater than 5 mm. Subsequently, the periphery of the clad slab is sealed welded, leaving an unwelded area of ​​a specific size. Before welding, the slab is 10 -2 ~10 -3The material is subjected to a vacuum treatment at Pa. The slab is heated to 500-700°C and rolled, with a first-pass reduction of over 25%, a final-pass reduction of 15% or less, a total reduction of 60-70%, and a rolling speed of 0.1-1.0 mm / s. The patent application achieves prevention of diffusion and oxidation of impurity elements at high temperatures by employing a high-temperature permeability-resistant coating, thereby preventing the diffusion of elements such as carbon and nitrogen. In the example, Q235 steel and TA1 titanium were bonded, and the resulting clad plate exhibited shear strengths of 176 MPa, 181 MPa, and 182 MPa.

[0011] The two patent applications mentioned above primarily aim to avoid the formation of brittle titanium compounds by providing an additional nickel-based alloy separation layer between titanium and carbon steel.

[0012] Chinese patent application CN201811327623.4 discloses a titanium-steel-titanium clad sheet and a method for producing the same. The method involves sandwiching a carbon steel sheet between two titanium sheets of the same size and then integrally bonding the three layers by hot clad rolling using an irreversible high-pressure hot rolling mill. After rolling, the rolled clad sheet is heat-treated, which includes primary annealing at 500-600°C for 20-60 minutes and recrystallization annealing at 680-700°C for 30-120 minutes. Finally, the product is obtained by straightening, planarizing, shearing, and forming. The patent application mainly describes a method for producing clad titanium steel sheets without using hot rolling clading. However, because an irreversible rolling mill is used, only single-pass rolling production is possible, and heat treatment is also required. The examples mainly focus on the method for producing steel strips, and do not mention the performance of the product after clading.

[0013] Chinese patent application CN201510543767.3 discloses a method for manufacturing titanium-steel clad sheets. The titanium-steel clad sheets obtained by this method have high bonding strength. The patent application includes: fixing a titanium sheet between two ordinary carbon steel sheets or slabs, welding the perimeter of the assembly in a vacuum environment, heating the clad slab to 850-900°C for 120-360 minutes, controlling the rolling process with an initiation rolling temperature of 800°C or higher and a finish rolling temperature of 700°C or lower, and controlling the deformation of each pass to 20-30% and the total deformation during rolling to ≥90%. This high-reduction rolling process destroys brittle intermetallic compounds formed at the interface, thereby reducing their impact on the bonding interface. After rolling, the obtained titanium-steel clad sheets achieve a bonding strength exceeding 240 MPa. However, because the patent application requires a high pass reduction ratio and total deformation, cracks are likely to occur in the end welds during the rolling process, which can impair the vacuum and make it unsuitable for interfacial bonding.

[0014] Chinese patent application CN201610994234.1 discloses a method for manufacturing titanium-steel clad sheets, the method including an annealing technique for manufacturing titanium steel sheets. First, titanium sheets and steel sheets are assembled to form a symmetrical multilayer clad slab having a steel sheet-titanium sheet-separating agent-titanium sheet-steel sheet structure. Cladding is carried out by roll cladding or explosion cladding. The clad slab is annealed and pickled using a continuous annealing and pickling line. First, it is heated to 500-750°C to recrystallize the titanium sheets of the core, and then heated to 950-1050°C to recrystallize the steel sheets of the base. The object of the patent application is to simultaneously achieve the properties of the cladding material and the base material by two-stage heat treatment. However, two-stage heat treatment can result in excessive diffusion of titanium, iron, and carbon, resulting in the generation of brittle materials such as intermetallic compounds of iron and titanium, as well as titanium carbides, which reduce the interfacial shear strength.

[0015] Chinese Patent Application CN201710996925.X discloses a thin clad double-sided titanium-steel clad sheet and a method for manufacturing the same. The method achieves good cladding between titanium and steel by using thick slab assembly and high reduction rolling technology. The patent application covers a double-sided titanium clad sheet composed of a titanium cladding layer, a base layer, and a titanium cladding layer. The titanium cladding layer is formed of TA2 material, in which the titanium cladding layer has a thickness of 0.2 to 1 mm. The slab assembly is laminated in the following top-to-bottom order: cover plate, titanium cladding material, carbon steel base, titanium cladding material, and cover plate in the center. After vacuuming in a vacuum chamber, the periphery seam of the assembly is 1.0 × 10 -2 ~4.5×10 -2 The clad slab is sealed and welded by a vacuum electron beam at a vacuum of Pa. The sealed and welded clad slab is heated to 900-920°C and held for a time calculated as 1 minute / mm × the total thickness of the clad slab. The starting rolling temperature is 880-900°C, the finishing rolling temperature is 800°C or higher, and then it is cooled to room temperature by air cooling. The single-pass reduction ratio is ≥15%, the reduction ratio for the first three passes is ≥20%, and the total reduction ratio is ≥80%. The clad sheet obtained after rolling is subjected to trimming, sheet splitting, and surface grinding to obtain a double-sided titanium-steel clad sheet. In this patent application, the iron-titanium and titanium-carbon compounds formed at the clad interface are crushed, refined, and dispersed within the clad interface by the application of surface cleaning treatment of the clad slab, the covering and air separation effect of the cover plate, controlled rolling temperature, and high pressure reduction ratio. This improves the distribution of the compound, further ensuring bonding quality and performance stability, resulting in a shear strength of 241 MPa.

[0016] Chinese patent application CN201710983322.6 discloses a thin clad titanium-steel clad sheet and a method for manufacturing the same, which employs a two-layer structure of titanium and carbon steel cladding. The slab assembly method and heating process are similar to those of Chinese patent application CN201710996925.X, with an initial rolling temperature of 880-900°C, a single-pass reduction ratio of 25-30%, and a total reduction ratio of ≥85%. While controlling the single-pass reduction ratio and total reduction ratio, the thickness of the titanium-steel clad sheet is limited to 3-16 mm. The finish rolling temperature is 800°C or higher, after which it is cooled to room temperature by air cooling. The titanium-steel clad sheet is obtained after surface treatment, and the titanium cladding layer has a thickness of ≤1 mm. The patent application employs a symmetrical slab assembly method and improves bonding quality by sealing titanium within the carbon steel sheet by seal welding. After rolling, the steel sheet achieves a shear strength of 238 MPa or higher, and the bonding rate of the cladding interface is 100%. The carbon steel layer meets the requirements of the Chinese national standard Q345 grade carbon steel.

[0017] However, the two aforementioned patent applications do not specify detailed designs for the cladding and base layers, only referring to tensile properties and shear strength. While the required pass reduction ratio and total reduction ratio for the cladding layer are relatively high, performance indicators such as corrosion resistance of the material, low-temperature impact performance of the base layer material, and yield ratio are not controlled, and thus do not meet the requirements for steel used in building structures.

[0018] In summary, the aforementioned patent application primarily describes a method for manufacturing clad steel sheets, and the specific examples briefly explain properties such as interfacial shear strength and tensile properties. Steel for steel structures in areas with ocean waves and spray must not only be resistant to corrosion in such areas, but also meet the requirements for structural steel properties, as well as the aforementioned low yield ratio and corresponding low-temperature impact properties, in order to guarantee the safety of the structure. However, the aforementioned patent application does not provide composition and process designs regarding the corrosion rate of the corrosion-resistant layer, yield ratio, low-temperature impact properties, etc., and therefore cannot ensure that the requirements for using highly corrosion-resistant steel sheets for steel structures in environments with ocean waves and spray are met. [Overview of the Initiative]

[0019] overview In light of the shortcomings of the prior art described above, one of the objectives of this disclosure is to provide hot-rolled steel strips for building steel structures and a method for manufacturing the same. The hot-rolled steel strips for building steel structures according to this disclosure can satisfy the corresponding strength level requirements for the mechanical properties of the base layer (carbon steel) without impairing the corrosion resistance of the corrosion-resistant layer itself, and the base layer exhibits excellent yield ratio and low-temperature impact toughness.

[0020] Accordingly, in one aspect, the present disclosure provides hot-rolled steel strips for building structures, wherein the hot-rolled steel strips include a base layer, a corrosion-resistant layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer.

[0021] The base layer contains, in addition to iron and other unavoidable impurities, the following chemical elements in mass percent: carbon: 0.03-0.13%, silicon: 0.15-0.35%, manganese: 1.00-1.50%, P: 0.0005-0.003%, S: 0.0005-0.01%, Cr: 0.10-0.65%, Ni: 0.2-1.0%, Cu: 0.10-0.25%, Al: 0.020-0.050%, Ti: 0.0090-0.0160%, Nb: 0.060-0.100%, N: 0.0005-0.0050%, and V: 0.08-0.25%.

[0022] The corrosion-resistant layer is made from industrial-grade pure titanium, preferably TA1, TA2, TA3, or TA4.

[0023] Preferably, the base layer has a chemical composition that further satisfies the following relationship: 0.32% ≤ Cu + Ni ≤ 1.15%; and 2(C+N)≦Ti+Nb+Cr+V≦0.90%.

[0024] Preferably, the base layer contains the following chemical elements in mass percentages: C: 0.03 to 0.13%, Si: 0.15 to 0.35%, Mn: 1.00 to 1.50%, P: 0.0005 to 0.003%, S: 0.0005 to 0.01%, Cr: 0.10 to 0.65%, Ni: 0.2 to 1.0%, Cu: 0.10 to 0.25%, Al: 0.020 to 0.050%, Ti: 0.0090 to 0.0160%, Nb: 0.060 to 0.100%, N: 0.0005 to 0.0050%, V: 0.08 to 0.25%, and the balance is Fe and other inevitable impurities.

[0025] Preferably, the base layer has a microstructure of ferrite + bainite + martensite, in which the content of bainite + martensite is 5% to 15%, and the average grain size of ferrite is ≥ grade 8.5.

[0026] Preferably, the yield strength of the base layer is ≥ 460 MPa, the tensile strength is ≥ 580 MPa, the yield ratio is ≤ 0.81 (preferably ≤ 0.75), and the impact energy at -40°C is ≥ 190 J.

[0027] Preferably, the corrosion-resistant layer has a microstructure of single equiaxed α-Ti. Preferably, the corrosion rate of the corrosion-resistant layer against sea-wave spray is ≤ 0.006 mm / year.

[0028] Preferably, the interface transition layer has a thickness of ≤ 8 μm, an average grain size of 15 to 40 μm, contains (Ti,Nb)C precipitation particles of < 120 nm, and its interface shear strength is ≥ 268 MPa.

[0029] The interface transition layer of the hot-rolled strip steel according to the present disclosure shows 100% metallurgical bonding and highly aggregated atoms, and the interface transition layer has a microstructure of fine particles (average particle size 15 to 40 μm).

[0030] Preferably, the thickness of the hot-rolled steel strip for building structures is 1 to 16 mm. The base layer of the hot-rolled steel strip for building structures according to this disclosure has a yield strength of ≥460 MPa, a tensile strength of ≥580 MPa, a yield ratio of ≤0.81 (preferably ≤0.75 or less), and an impact energy of ≥190 J at -40°C; the corrosion rate of the corrosion-resistant layer against seawater spray is ≤0.006 mm / year; and the thickness of the interface transition layer is ≤8 μm, and the interface shear strength is ≥268 MPa. The hot-rolled steel strip according to this disclosure can meet the corrosion resistance requirements for use in environments with seawater spray, has excellent mechanical properties and high economic efficiency, and is suitable for appropriate use in steel structures such as steel piles for facilities such as port terminals and offshore oil platforms.

[0031] This disclosure employs a low-carbon trace alloy composition design to achieve excellent bonding between titanium and carbon steel without the addition of a metal separation layer, effectively controlling the thickness of the interface transition layer. In this way, the mechanical properties of the base layer (carbon steel) meet the requirements of the corresponding strength class without reducing the corrosion resistance of the corrosion-resistant layer itself.

[0032] In another aspect, this disclosure provides a method for manufacturing hot-rolled steel strips for the above-mentioned building structures, the method being carried out in the following order: 1) Smelting and casting Based on the above compositions of the base layer and corrosion-resistant layer, the base layer and corrosion-resistant layer are smelted and cast into slabs; 2) Slab assembly The slab surface for the base layer and corrosion-resistant layer is ground and polished, and peripheral welding sealing is performed along the contact surfaces of the slab to form a clad slab including the base layer and corrosion-resistant layer; after welding sealing, the joint interface is vacuum-treated; 3) The clad slab is heated and rolled to form a steel strip, and within Heat the clad slab to 900-1000°C; Rough rolling is performed at a temperature of ≥860°C; finish rolling is performed at a temperature of 760-850°C, preferably 780-850°C; the pass reduction ratio is 5-20%, preferably 10-15%; and the cumulative reduction ratio is ≥88%. 4) Cooling Hot-rolled steel strip is produced by cooling the steel strip to a temperature of 300-450°C and then winding it up at this temperature. Includes the process.

[0033] Preferably, in step 2), the thickness of the corrosion-resistant layer is 1 to 10% of the thickness of the clad slab. Preferably, the thickness of the interface transition layer formed between the base layer and the corrosion-resistant layer in step 3) is ≤ 8 μm.

[0034] Preferably, in step 4), the cooling includes two stages of cooling, in which, in the first stage, after leaving the rolling mill stand, the steel strip is cooled to 700-750°C at a cooling rate of 2-10°C / second; and in the second stage, the steel strip is cooled to 300-450°C at a cooling rate of 30-50°C / second.

[0035] The manufacturing method according to this disclosure, particularly through the control of the heating, rolling, and cooling processes, results in a base layer of the steel strip exhibiting a low yield ratio and good low-temperature impact toughness, while the corrosion-resistant layer possesses excellent corrosion resistance and high bonding strength. [Brief explanation of the drawing]

[0036] [Figure 1] Figure 1 is a schematic diagram of the interlayer structure of a hot-rolled steel strip for building structures according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic diagram of the interlayer structure of a hot-rolled steel strip for building structures according to another embodiment of the present disclosure. [Figure 3] Figure 3 is a photograph showing the microstructure of the corrosion-resistant layer in Example 3. [Figure 4] Figure 4 is a scanned image of the interface transition layer between the base layer and the corrosion-resistant layer in Example 3. [Figure 5] Figure 5 is a photograph of the microstructure of the base layer in Example 3. [Modes for carrying out the invention]

[0037] Detailed explanation Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art relating to this disclosure. The terms used herein are intended solely to describe specific embodiments and are not intended to limit the disclosure.

[0038] In this specification, "bainite + martensite content" refers to the area ratio of the "bainite + martensite" microstructure in the photographs observed by metallographic analysis.

[0039] In this specification, “industrial-grade pure titanium” refers to dense metallic titanium with a titanium content of at least 99%, and containing small amounts of impurities such as iron, carbon, oxygen, nitrogen, and hydrogen. “TA1, TA2, TA3, and TA4” indicate grades of industrial-grade pure titanium. This grading standard classifies pure titanium by purity level (i.e., impurity content) based on GB / T3620.1-2016 “Nomenclature and Composition of Titanium and Titanium Alloys”.

[0040] In this specification, "yield ratio" refers to the ratio of the yield strength to the tensile strength of steel, and its magnitude reflects the steel's ability to avoid stress concentration during plastic deformation.

[0041] In this specification, yield strength and tensile strength are measured in accordance with GB / T 6396-2008 "Clad steel sheets - Mechanical and technical testing" and GB / T 228-2010 "Metallic materials - Tensile testing - Test methods at room temperature".

[0042] In this specification, the impact energy KV2 / J (longitudinal) at -40°C is measured according to GB / T 6396-2008 "Clad steel sheets - Mechanical and technical tests" and GB / T 229-2020 "Metallic materials - Charpy pendulum impact test method".

[0043] In this specification, particle size grading is performed as follows: The particle size of ferrite microstructures in stainless steel and carbon steel is graded using the intercept method according to GB / T 6394-2017, “Determination of Estimation of Average Particle Size of Metals.”

[0044] In this specification, the corrosion rate against ocean wave spray is measured as follows: A coupon test specimen of clad steel plate is placed in an area of ​​ocean wave spray in the South China Sea for 6 months, and then the corrosion is observed and recorded. First, the coupon is washed and weighed. The volume lost is obtained by dividing the weight lost by the density. Then, the thickness lost is obtained by dividing the volume lost by the exposed area of ​​the coupon.

[0045] In this specification, interfacial shear strength is measured according to GB / T 6396-2008 "Clad steel sheets - Mechanical and technical tests".

[0046] In this specification, the metals in the base layer and corrosion-resistant layer undergo recrystallization and grain growth under high temperature and pressure. During this process, some crystal grains pass through the interface. Simultaneously, due to differences in elemental content on both sides of the interface, metal elements diffuse from high-concentration regions to low-concentration regions at high temperatures. These two factors combine to form an interfacial transition layer. In the compositional design of the base layer of hot-rolled steel strip for building steel structures according to this disclosure:

[0047] C:C has a solid solution strengthening effect in steel, significantly improving its strength. However, excessively high C content adversely affects weldability and toughness. More importantly, if the C content is too high, C diffuses toward the cladding interface, forming a large amount of large granular TiC hard phase in the interface transition layer, thus reducing the strength of the cladding interface. Therefore, a low C content is necessary to ensure the shear strength of the interface. Changes in C content have a smaller effect on yield strength compared to tensile strength of steel. Therefore, while ensuring the formability and weldability of the product, appropriately increasing the C content is beneficial in reducing the yield ratio of the steel. Accordingly, the C content in the base layer composition of this disclosure is controlled to 0.03% to 0.13%.

[0048] Si: Adding Si to steel effectively deoxidizes it and improves its purity. Furthermore, Si has a solid solution strengthening effect in steel, increasing its strength and hardness. However, excessively high Si content adversely affects the weldability of the material. Therefore, the Si content in the base layer composition of this disclosure is controlled to 0.15% to 0.35%.

[0049] Mn:Mn is the most cost-effective matrix strengthening element. Mn lowers the austenite transformation temperature, delays the pearlite transformation, refines ferrite grains, and improves the strength of the steel. At the same time, Mn can also eliminate the influence of sulfur on the steel. However, excessively high Mn content can easily lead to the formation of segregation zones and martensite microstructures, adversely affecting the toughness of the steel. Therefore, the Mn content in the base layer composition of this disclosure is controlled to 1.00% to 1.50%.

[0050] Al: Al is added in excess to the steel primarily as a deoxidizing element to ensure that the oxygen content in the steel is kept as low as possible. After deoxidation, the excess Al combines with the nitrogen element in the steel to form AlN precipitates. During heating, AlN suppresses austenite grain growth, refines the austenite grains, and improves the strength and toughness of the matrix. At the same time, the formation of AlN fixes some nitrogen in the matrix, reducing the diffusion of interstitial nitrogen atoms to the cladding interface in the carbon steel base layer and the formation of hard TiN in the interfacial transition layer (which reduces the interfacial shear strength of the cladding plate). It also reduces the amount of Ti and Nb to be added, thereby lowering the overall cost. Therefore, the Al content in the base layer composition of this disclosure is controlled to 0.020% to 0.050%, preferably 0.020% to 0.030%.

[0051] Ti:Ti forms stable TiN or Ti(N,C) at high temperatures, fixing C and N, preventing the diffusion of interstitial C and N atoms to the interface in the carbon steel base layer, as well as the formation of hard TiN or Ti(N,C) precipitates in the interface transition layer, thereby obtaining a clad plate with high interfacial shear strength. At the same time, during heating, TiN suppresses austenite growth, refines austenite grains, and improves the strength and toughness of the matrix. During subsequent welding, TiN suppresses austenite grain growth, particularly in the heat-affected zone (HAZ) adjacent to the weld molten boundary, improving the toughness of the weld HAZ, thereby meeting the requirements of a high welding heat input process. By suppressing the diffusion of C and N to the interface, the strength of the low-carbon matrix can be improved, resulting in a clad steel strip with high interfacial shear strength. Therefore, the Ti content in the base layer of this disclosure is controlled to 0.0090% to 0.0160%.

[0052] Nb:Nb exists in the steel in the form of solid solution Nb and Nb(C,N), and has the effects of solid solution dragging and precipitate pinning during the recrystallization process. The addition of a small amount of Nb to the carbon steel for the base layer is mainly to raise the recrystallization temperature, which results in grain refinement in the recrystallized and non-recrystallized regions after rolling, contributing to improved low-temperature impact toughness of the carbon steel for the base layer. Due to the effect of the Nb(C,N) precipitate phase, prior austenite grains are refined, thus promoting the formation of fine recrystallized grains, achieving a desirable combination of high strength and high toughness. At the same time, Nb can fix interstitial C and N atoms in the matrix, suppressing the diffusion of C and N to the interface. This results in a clad plate with high interfacial shear strength. Therefore, the Nb content in the base layer of this disclosure is controlled to 0.060% to 0.100%.

[0053] Cu:Cu exhibits a solid solution strengthening effect, and as the Cu content increases, the room-temperature impact toughness of the steel slightly improves. Therefore, the Cu content in the base layer of this disclosure is controlled to 0.10% to 0.25%.

[0054] N:N reacts with Ti and Al to form second-phase grains, refining the austenite grains and improving the strength and toughness of the matrix. However, if the N content is too high, the amount of TiN produced increases, leading to grain coarsening, which can adversely affect the plasticity and toughness of the carbon steel. Therefore, the N content in the base layer of this disclosure is controlled to 0.0005% to 0.0050%.

[0055] Ni:Ni is an element that stabilizes austenite and has a certain effect on improving toughness and strength. Adding Ni to steel can significantly improve the low-temperature impact toughness of the steel. However, since Ni is expensive, adding too much Ni increases the cost of the clad plate. Therefore, an appropriate amount of Ni is added to the base layer of this disclosure, and the Ni content in the base layer of this disclosure is controlled to 0.2% to 1.0%.

[0056] Cr:Cr is a strong carbide-forming element. Its diffusion rate in austenite is low, and it also inhibits the diffusion of C. During low-temperature processes, Cr and C form fine carbides, which have a precipitation strengthening effect. At the same time, Cr fixes interstitial C and N atoms in the matrix, suppressing the diffusion of C and N to the interface, and as a result the clad plate has high interfacial shear strength. However, Cr in steel increases the strength of the matrix but decreases its toughness. Therefore, the Cr content in the base layer composition of this disclosure is controlled to 0.10% to 0.65% to achieve an optimal balance between strength and toughness.

[0057] V:V is a strong carbonitride-forming element. When V is added to steel in combination with Ti and Nb, it forms fine composite carbonitrides, which broadens the precipitation temperature range, effectively prevents austenite grain growth, suppresses recrystallization, and improves the strength and toughness of the carbon steel for the base layer. At the same time, the carbonitrides of V have a low precipitation temperature; by precipitation during phase transformation, they effectively suppress ferrite grain growth and strengthen the ferrite matrix. Therefore, an appropriate amount of V is added to the base layer of this disclosure, and the V content in the base layer is controlled to 0.08%~0.25%.

[0058] In the hot-rolled steel strips for building structures according to this disclosure, S and P are both unavoidable impurity elements, and their content should be kept as low as possible. However, considering the actual steelmaking capacity of the steel mill, the content of S and P in the base layer composition of this disclosure is controlled to: S ≤ 0.010%; and P ≤ 0.003%.

[0059] Further chemical composition design of the base layer of hot-rolled steel strip for building steel structures according to this disclosure: Both Cu and Ni can improve the toughness of the base layer, and their combined addition has a particularly significant effect. Simultaneously, the addition of Ni can reduce the diffusion rate of C in the steel and suppress the diffusion of C to the interface. Therefore, to obtain better properties, the Cu and Ni content in the base layer composition of this disclosure preferably further satisfies: 0.32% ≤ Cu + Ni ≤ 1.15%, which contributes to controlling the thickness of the interface transition layer to ≤ 8 μm.

[0060] Ti, Nb, Cr, and V are all strong carbonitride-forming elements, and they can form corresponding carbonitrides in the carbon steel for the base layer. This can fix the interstitial atoms in the base layer and prevent the diffusion of interstitial atoms C and N to the interface, which would form aggregated carbonitrides of coarse particles in the interfacial transition layer. This helps to control the interfacial transition layer to ≤8 μm, thereby improving the interfacial shear strength. At the same time, Ti, Nb, and Cr have the effect of refining the grains of the carbon steel for the base layer and improving toughness at different stages of hot rolling. Therefore, to obtain better properties, the content of Ti, Nb, Cr, and V in the base layer composition of this disclosure preferably further satisfies: 2(C+N) ≤ Ti+Nb+Cr+V ≤ 0.90%.

[0061] The corrosion-resistant layer in this disclosure uses industrial-grade pure titanium, preferably TA1, TA2, TA3, and TA4. The composition of the industrial-grade pure titanium conforms to the GB / T3620.1-2016 standard, "Nomenclature and composition of titanium and titanium alloys."

[0062] The method for manufacturing hot-rolled steel strip for building structures according to this disclosure is as follows: 1) Smelting and casting Based on the above compositions of the base layer and corrosion-resistant layer, the materials for the base layer and corrosion-resistant layer are smelted and cast into slabs; 2) Slab assembly The surface of the slab for the base layer and corrosion-resistant layer is ground and polished, and peripheral welding sealing is performed along the contact surfaces of the slab to form a clad slab including the base layer and corrosion-resistant layer; after welding sealing, the bonding interface is vacuum-treated; 3) The clad slab is heated and rolled to form a steel strip, and within Heat the clad slab to 900-1000°C; Rough rolling is performed at a temperature of ≥860°C; finish rolling is performed at a temperature of 760-850°C; the pass reduction ratio is 5-20%; and the cumulative reduction ratio is ≥88%. 4) Cooling Hot-rolled steel strip is produced by cooling the steel strip to a temperature of 300-450°C and then winding it up at this temperature. Includes the process.

[0063] Preferably, in step 4), the cooling includes two stages, in which, in the first stage, after leaving the rolling mill stand, the steel strip is cooled to 700-750°C at a cooling rate of 2-10°C / second; and then in the second stage, the steel strip is cooled to 300-450°C at a cooling rate of 30-50°C / second.

[0064] Preferably, in step 2), the thickness of the corrosion-resistant layer is 1 to 10% of the total thickness of the clad slab. Preferably, in step 3), the pass reduction ratio used during rolling is 10-15%.

[0065] Manufacturing method according to this disclosure: 1) Smelting: P and S elements reduce the fracture toughness of steel. Therefore, P and S should be controlled to low levels during the smelting process to improve slab quality. Preferably, clean steelmaking technology is adopted to reduce the gas and inclusion content in the steel, thereby improving the overall performance of the steel, especially its resistance to layered cracking.

[0066] 2) Slab assembly: The thickness of the corrosion-resistant layer is preferably 1-10% of the total thickness of the clad slab. The slabs for the corrosion-resistant layer slab and the carbon steel base layer are pre-treated, peripheral welding seals are applied to the contact surfaces of the slabs, and vacuum treatment is performed on the joint interfaces after welding seals. Vacuum treatment can prevent oxidation of the surface of the corrosion-resistant layer and is an important factor in ensuring the corrosion resistance of the corrosion-resistant layer in areas of ocean wave spray. It also ensures that defects such as edge cracking and crushing of the corrosion-resistant layer are prevented during subsequent high cumulative reduction deformation.

[0067] 3) Heating: In the case of single carbon steel, the heating temperature of the slab is generally controlled to 1000-1250°C. This promotes the dissolution and sufficient diffusion of precipitates in the steel, promotes the homogenization of elements in the slab, and allows trace alloying elements to exert a strengthening effect in the steel. In the case of single industrial pure titanium sheets, the heating temperature is generally controlled to 850-1000°C. If the heating temperature is too high, β-phase transformation occurs, the β-phase grows rapidly, and the properties of industrial pure titanium deteriorate. High heating temperatures allow for sufficient diffusion of elements and promote the achievement of 100% metallurgical bonding at the interface thereafter. However, if the heating temperature is excessively high, the tendency for austenite grains to coarse increases, making subsequent rolling control more difficult. More importantly, the diffusion of C, N, Ti, and Fe to the interface is accelerated, forming thick brittle precipitates and intermetallic compounds at the interface, resulting in a thick interfacial transition layer and a decrease in interfacial shear strength. This promotes the diffusion of N, Ti, and Fe into the interface, forming thick brittle precipitates and intermetallic compounds at the interface. This results in a thicker interface transition layer and a decrease in interface shear strength. Considering these factors, the method according to this disclosure employs a lower heating temperature than conventional carbon steel production, controlling the heating temperature to 900-1000°C.

[0068] 4) Rolling: The rough rolling temperature is controlled to 860°C or higher. In the high-temperature rough rolling zone, a high reduction ratio is applied to completely recrystallize the microstructure and refine the grain size, thereby improving the strength and toughness of the material. In the non-recrystallized zone of finish rolling, controlled rolling is performed, and at this stage, austenite recrystallization no longer occurs. With an appropriate reduction ratio and finish rolling temperature, deformation energy and deformation dislocations are accumulated, which forms high-density deformation zones within the austenite grains, increasing the number of nucleation sites for ferrite phase transformation, further refining the grain size after matrix transformation, and improving the strength and toughness of the material. At the same time, the deformation during this stage induces the precipitation of carbonitrides of Nb, Ti, Cr, and V, increasing the strength of the matrix and suppressing the diffusion of C into the interface, thereby preventing the formation of excessively thick TiC at the interface and a decrease in interfacial shear strength. The pass reduction ratio is controlled to 5%~20%, and the cumulative reduction ratio is controlled to ≥88%. Preferably, the finish rolling is controlled to be carried out at a temperature of 780-850°C, thereby ensuring the corrosion resistance of titanium while avoiding rolling of the base layer in the two-phase region. As a result, a base layer with a ferrite-bainite-martensite microstructure is obtained, in which the average grain size of ferrite is ≥8.5 and the bainite-martensite content is 5%-15%. During the rolling process, the corrosion-resistant layer and the base layer experience only metallurgical bonding and the necessary size changes, and no changes occur in the composition of the corrosion-resistant layer and the base layer.

[0069] 5) Cooling: The type, size, and content of microstructure after rolling can be adjusted by controlling the initial cooling, finish cooling, and cooling rate. If the cooling rate is too high, a large amount of bainite and martensite will form. In this case, the martensite phase has a structure with low toughness and a high yield ratio, which adversely affects the properties of the steel sheet. If the cooling rate is too low, a large amount of coarse ferrite microstructure will be generated. This coarse ferrite microstructure promotes crack propagation, resulting in a decrease in impact properties. Therefore, the cooling rate should be appropriately controlled. By controlling the finish rolling temperature during finish rolling, the formation of abnormally coarse microstructure due to rolling in the two-phase region can be avoided. At the same time, this allows for rapid cooling to the phase transformation temperature after rolling, which further suppresses microstructure growth, refines the crystal grains, improves the strength and low-temperature impact toughness of the material, and forms a hard phase microstructure of 5% or more to ensure strength. Preferably, a step cooling method is employed. After the steel strip leaves the rolling mill stand, it is first cooled to the ferrite phase transformation temperature at a cooling rate of ≤10°C / s, then rapidly cooled to 350-450°C at a cooling rate of 30°C-50°C / s, and then wound up. This yields a small amount of bainite and martensite microstructure, enables microstructure recovery during the winding process, promotes the precipitation of V carbonitrides, and ensures that the base layer has a low yield ratio and high low-temperature impact toughness.

[0070] If the corrosion-resistant layer is too thick, it will affect the mechanical properties and production costs of the material. If the corrosion-resistant layer is too thin, it will reduce the corrosion resistance and service life of the material. Preferably, during the assembly process, the thickness of the corrosion-resistant layer should be controlled to 1-10% of the total thickness of the cladding plate.

[0071] A corrosion-resistant layer is clad with a base layer, and a rolling process is performed to form a corrosion-resistant layer on the surface of the base layer (i.e., carbon strip steel) that is resistant to corrosion in areas with ocean waves and spray, in accordance with the design of the composition and thickness ratio of both layers. As a result, the final hot-rolled strip steel for building structures according to this disclosure is obtained, which exhibits corrosion resistance in areas with ocean waves and spray, excellent mechanical properties, and high economic efficiency. This strip steel can then be processed into structural members and effectively used as members of steel structures used in environments with ocean waves and spray.

[0072] Compared to existing technologies, the hot-rolled steel strip for building structures according to this disclosure offers the following advantages: The hot-rolled steel strip for building structures according to this disclosure is designed with a low-carbon trace alloy composition, achieving excellent bonding between titanium and carbon steel without the addition of a metal separation layer, effectively controlling the thickness of the interfacial transition layer, and thus the mechanical properties of the base layer (carbon steel) can meet the requirements of the corresponding strength grade without reducing the corrosion resistance of the corrosion-resistant layer itself.

[0073] The hot-rolled steel strip for building structures according to this disclosure reduces the formation of TiC compounds in the interfacial transition layer and carbonitrides in the base layer by reducing the carbon content, thereby inhibiting grain growth and improving the low-temperature impact toughness of the base layer. At the same time, the addition of trace alloying elements in addition to a rational rolling and cooling process solves the problem of reduced material strength in the case of low carbon, achieving a yield strength of ≥460 MPa and tensile strength of ≥580 MPa in the base layer, while also achieving a yield ratio of ≤0.81 and an impact energy of ≥190 J at -40°C. All of these exceed the performance requirements of the Chinese national standard GB / T 19879-2015 "Steel plates for building structures".

[0074] Chinese patent application CN201210260231.7 describes how to obtain a titanium-steel clad sheet with an interfacial bonding rate of 99.6% to 100% by adding a nickel plate as a separator between the clad layer and the base layer to prevent TiC formation at the interface. In contrast, the hot-rolled steel strip for building structures according to this disclosure reduces nickel addition through a low-carbon and trace alloy design, thereby lowering manufacturing costs. At the same time, it also achieves perfect metallurgical bonding with a 100% interfacial bonding rate by optimizing processes such as heating and rolling, forming a transition layer microstructure of a certain thickness and reducing the generation of brittle TiC in the interfacial transition layer.

[0075] In Chinese patent application CN201710769999.X, the slab heating temperature was 500-700°C, the total reduction rate was 60-70%, and the maximum interfacial shear strength of the produced steel strip was 182 MPa. In contrast, the inventors have given full consideration to the impact of the high-temperature phase transformation problem of industrial pure titanium for the corrosion-resistant layer on corrosion resistance, as well as the control of the strength and toughness of the carbon steel for the base layer, along with the overall design of the low-carbon trace alloy design and processing technology. The heating temperature of the clad slab is set to 900-1000°C. At this temperature, phase transformation of the corrosion-resistant layer is prevented, and sufficient dissolution of precipitates in the carbon steel for the base layer is ensured, thereby refining the grain size of the base layer during controlled rolling and improving the strength and toughness of the base layer. Furthermore, the cumulative reduction rate is controlled to ≥85% to break the brittle phase in the interfacial transition layer and improve the interfacial shear strength.

[0076] Chinese patent applications CN201210260231.7 and CN201710769999.X primarily avoid the formation of brittle Ti compounds by providing an additional nickel-based alloy separation layer between titanium and carbon steel. In contrast, this disclosure achieves perfect metallurgical bonding with a 100% interfacial bonding rate through composition and process design without adding a separation layer. Furthermore, the hot-rolled steel strip for building structures according to this disclosure differs from the two aforementioned patent applications in the method of slab assembly and also significantly differs from the two aforementioned patent applications in the material of the carbon steel for the base layer.

[0077] The process conditions of this disclosure ensure both the corrosion resistance of the industrial pure titanium in the corrosion-resistant layer and the mechanical properties of the base layer, solving the conventional problem of incompatibility of processing windows due to the large differences between titanium and carbon steel. At the same time, the elements of the base layer and the corrosion-resistant layer are controlled and sufficiently diffused to form an interfacial transition layer of ≤8 μm. This layer has a fine grain microstructure with an average particle size of 15-40 μm and contains (Ti,Nb)C precipitate particles of <120 nm, which enhances the interfacial bonding properties and ensures an interfacial shear strength of ≥268 MPa, which is significantly higher than the interfacial shear strength of 182 MPa in Chinese patent application CN201710769999.X.

[0078] The process described in Chinese Patent Application CN201811327623.4 achieves cladding by warm rolling, which requires a subsequent two-stage heat treatment including primary annealing at 500-600°C for 20-60 minutes and recrystallization annealing at 680-700°C for 30-120 minutes. This process encompasses a method for producing non-hot-rolled clad titanium strip steel, which is entirely different from the manufacturing method described herein.

[0079] The process described in Chinese patent application CN201510543767.3 employs a heating temperature of 850-900°C, a finish rolling temperature of 700°C or less, a single-pass reduction ratio of 20-30%, and a total reduction ratio of ≥90%. The shear strength of the titanium-steel clad plate is ≥240 MPa. Both the pass reduction ratio and total reduction ratio required in this patent application are very high, making end weld cracking likely to occur during rolling, impairing the vacuum state, making cladding difficult, and consequently reducing rolling stability. In contrast, the pass reduction ratio in this disclosure is controlled to 5-20%, which effectively prevents weld cracking during rolling, ensures the vacuum level inside the slab, and as a result improves interfacial shear strength, improving rolling stability and success rate.

[0080] Chinese patent application CN201610994234.1 relates to a method for manufacturing titanium-steel clad sheets. First, titanium sheets and steel sheets are assembled to form a symmetrical multilayer assembled clad slab of steel sheet-titanium sheet-separating agent-titanium sheet-steel sheet, which is then clad by rolling cladding or explosive cladding; the clad slab is then annealed and pickled in a continuous annealing and pickling line, first heated to 500-750°C to recrystallize the core titanium sheet, and then heated to 950-1050°C to recrystallize the base steel sheet. However, this application does not specifically describe the rolling process, nor the corrosion and microstructure properties of the resulting steel sheet. The process described in this patent application differs significantly from the method disclosed in terms of the manufacturing process. The method disclosed does not require two-stage heat treatment, thereby avoiding excessive diffusion of titanium, iron, and carbon elements, the formation of brittle materials such as iron-titanium intermetallic compounds and titanium carbide, and a decrease in interfacial shear strength.

[0081] The material of the corrosion-resistant layer of the titanium-steel clad sheet disclosed in Chinese patent application CN201710996925.X is TA2, and the thickness of the titanium clading layer is 0.2 to 1 mm. The manufacturing process is as follows: After seal welding, the clad slab is heated to 900 to 920°C and held for a certain period of time, the initial rolling temperature is 880 to 900°C, the finish rolling temperature is 800°C or higher, and it is air-cooled to room temperature. The resulting clad sheet achieves a shear strength of 241 MPa. In contrast, the method according to this disclosure employs a heating temperature of 900 to 1000°C and finish rolling is performed at a temperature of 750 to 850°C. The method according to this disclosure employs a two-stage cooling process for cooling. The method disclosed herein makes it possible to obtain a hot-rolled sheet having TA1, TA2, TA3, or TA4 as a corrosion-resistant layer, with a thickness of 1 to 10% of the total thickness of the clad slab, and an interfacial shear strength of ≥268 MPa.

[0082] The process disclosed in Chinese Patent Application CN201710983322.6 uses the same assembly mode and heating process as that of Chinese Patent Application CN201710996925.X, using a pass reduction ratio of 25-30% and a total reduction ratio of ≥85%. While controlling the pass reduction ratio and total reduction ratio, the thickness of the titanium-steel clad sheet is limited to 3-16 mm, a finish rolling temperature of 800°C or higher is adopted, and then it is cooled to room temperature by air cooling; surface treatment is performed to obtain a titanium-steel clad sheet with a titanium cladding layer thickness of ≤1 mm. In contrast, the method according to this disclosure uses a pass reduction ratio of 5-20% to control rolling stability and uses a two-stage cooling mode to ensure the type of microstructure of the material, thereby controlling the yield ratio and toughness. Furthermore, the method according to this disclosure differs significantly from the process disclosed in Chinese Patent Application CN20171098332.6 in terms of the thickness of the corrosion-resistant layer and the total thickness of the clad sheet.

[0083] The hot-rolled steel strips for building structures described herein can solve the challenges faced when using stainless steel or carbon steel in environments with ocean wave spray. Such hot-rolled steel strips for building structures can be effectively applied to the manufacture of steel structural members used in environments with ocean wave spray, such as steel structural members in facilities with ocean wave spray, such as port terminals and offshore oil platforms. Such hot-rolled steel strips for building structures meet the requirements of these structural members for corrosion resistance and mechanical properties in environments with ocean wave spray, significantly improving the applicability, safety, and durability of these structural members, resulting in great economic and social benefits. [Examples]

[0084] Examples The technical solutions of this disclosure will be described in more detail with reference to the following examples and accompanying drawings. It should be understood that the following examples are intended solely to illustrate specific embodiments of this disclosure and do not constitute any limitation on the scope of protection of this disclosure. All reagents used in the examples are commercially available. Experimental methods in the examples where no specific conditions are specified were performed according to conventional conditions known in the art or conditions recommended by the manufacturer.

[0085] Referring to Figures 1, 2, and 4, schematic diagrams of two interlayer structures of hot-rolled steel strip for building structures according to the present disclosure are shown, where 1 represents the base layer, 2 represents the corrosion-resistant layer, and 3 represents the interface transition layer.

[0086] Table 1 shows the compositions of the base layer and corrosion-resistant layer for Examples 1-8 and Comparative Examples 1-5. Examples 1-8 and Comparative Examples 1-5 were manufactured by the following process: 1) Smelting and casting Based on the respective compositions of the base layer and corrosion-resistant layer shown in Table 1, the base layer and corrosion-resistant layer were smelted and cast into slabs; 2) Slab assembly The slab surface for the base layer and corrosion-resistant layer was ground and polished, and peripheral welding sealing was performed along the contact surfaces of the slab to form a clad slab containing the base layer and corrosion-resistant layer; the joint interface after welding sealing was vacuum-treated; 3) The clad slab is heated and rolled to form a steel strip, and within The clad slab was heated to 900-1000°C; Rough rolling was performed at a temperature of ≥860°C; finish rolling was performed at a temperature of 760–850°C; pass reduction ratio was 5–20%; cumulative reduction ratio was ≥88%. 5) Cooling The steel strip was cooled in two stages to a temperature of 300-450°C, and then wound up at this temperature.

[0087] Table 2 shows the specific parameters of the manufacturing processes for Examples 1-8 and Comparative Examples 1-5.

[0088] Performance tests were then conducted on the base layers, corrosion-resistant layers, and clad steel sheets of Examples 1-8 and Comparative Examples 1-5. Yield strength and tensile strength were measured according to GB / T 6396-2008 "Clad Sheets - Mechanical and Technical Tests" and GB / T 228-2010 "Metallic Materials - Tensile Tests - Test Methods at Room Temperature". Impact energy KV2 / J (longitudinal direction) at -40°C was measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method". Grain size grading was performed as follows: The grain size of the ferrite microstructure of stainless steel and carbon steel was graded using the intercept method according to GB / T 6394-2017 "Determination of Estimation of Average Grain Size of Metals".

[0089] Table 3 shows the metallographic structure and mechanical properties of the base layer and corrosion-resistant layer, as well as the thickness and mechanical properties of the interface transition layer, in the clad steel sheets of Examples 1-8 and Comparative Examples 1-5.

[0090] Figure 3 shows the microstructure of the corrosion-resistant layer in Example 3. As shown in Figure 3, the microstructure of the corrosion-resistant layer in Example 3 was a single equiaxed α-Ti with an average grain size of 103.4 μm.

[0091] Figure 4 shows the interface transition layer of Example 3. As shown in Figure 4, the thickness of the interface transition layer was 7.6 μm, and the discontinuous fine particles within it were TiC with a size of less than 120 nm.

[0092] Figure 5 shows the microstructure of the base layer of Example 3. As shown in Figure 5, the microstructure of the carbon steel base layer of Example 3 was ferrite + bainite + martensite, with a volume fraction of bainite + martensite of 7.8%, and a ferrite grain size of ≥8.5.

[0093] Furthermore, the corrosion resistance of the clad steel sheets of Examples 1-8 and Comparative Examples 1-5 was tested, and the results are shown in Table 4. Specifically, the corrosion resistance was tested using the following method: Coupon test specimens of the clad steel sheets of Examples 1-8 and Comparative Examples 1-5 were placed in the South China Sea wave spray area (different locations, i.e., Scenes 1-8 were selected) for 6 months, and the corrosion state was observed and recorded.

[0094] In Comparative Examples 1-5, some properties of the clad steel sheets did not meet the requirements for use because the composition design and heat treatment conditions did not meet the requirements (performance parameters were not within the range defined in this invention). Specifically:

[0095] In Comparative Example 1, the pass reduction ratio and cumulative reduction ratio did not meet the process requirements of this disclosure; as a result, the particle size became coarser, the yield strength and impact energy of the base layer did not meet the requirements, and the corrosion resistance was poor.

[0096] In Comparative Example 2, the Ti content was too high; as a result, the impact properties did not meet the requirements, and the corrosion resistance was poor.

[0097] In Comparative Example 3, the winding temperature did not meet the process requirements of this disclosure, and the yield ratio did not meet the requirements.

[0098] In Comparative Example 4, without the addition of V, the cooling rate after leaving the rolling mill stand and the cooling rate in the second stage did not meet the process requirements of this disclosure, and the necessary precipitation strengthening effect was not achieved.

[0099] In Comparative Example 5, the heating temperature and finish rolling temperature did not meet the process requirements of this disclosure; the transition layer thickness was too large, the shear strength did not meet the requirements, and the corrosion resistance was poor.

[0100] In contrast to these, Examples 1-8 showed that the base layer exhibited a yield strength ≥ 460 MPa, tensile strength ≥ 580 MPa, yield ratio ≤ 0.81, and impact energy ≥ 190 J at -40°C; the corrosion-resistant layer exhibited a corrosion rate of ≤ 0.006 mm / year against ocean wave spray.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] It should be noted that the combinations of the technical features of this disclosure are not limited to those described in the claims or embodiments, and all technical features described in this disclosure can be freely combined in any way, provided they do not conflict with each other.

[0106] Furthermore, it should be noted that the embodiments described above are merely specific examples of the present disclosure. It is clear that the present disclosure is not limited to the above embodiments, and various similar modifications or variations are possible. Such modifications or variations can be directly obtained or readily conceivable by those skilled in the art from the content of the present disclosure, and all of them are within the scope of the present disclosure.

Claims

1. Hot-rolled steel strip for building structures, The hot-rolled steel strip comprises a base layer, a corrosion-resistant layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer; The base layer contains, in addition to iron and other unavoidable impurities, the following chemical elements in mass percent: C: 0.03–0.13%, Si: 0.15–0.35%, Mn: 1.00–1.50%, P: 0.0005–0.003%, S: 0.0005–0.01%, Cr: 0.10–0.65%, Ni: 0.2–1.0%, Cu: 0.10–0.25%, Al: 0.020–0.050%, Ti: 0.0090–0.0160%, Nb: 0.060–0.100%, N: 0.0005–0.0050%, V: 0.08–0.25%; and The corrosion-resistant layer is made from industrial-grade pure titanium, preferably TA1, TA2, TA3, or TA4. Hot-rolled steel strips for building structures.

2. The aforementioned base layer has the following relationship: 0.32% ≤ Cu + Ni ≤ 1.15%; and 2(C+N)≦Ti+Nb+Cr+V≦0.90% The hot-rolled steel strip for building structures according to claim 1, having a chemical composition that further satisfies the requirements.

3. The hot-rolled strip steel for building structures according to claim 1 or 2, wherein the base layer comprises, by mass percent, the following chemical elements: C: 0.03–0.13%, Si: 0.15–0.35%, Mn: 1.00–1.50%, P: 0.0005–0.003%, S: 0.0005–0.01%, Cr: 0.10–0.65%, Ni: 0.2–1.0%, Cu: 0.10–0.25%, Al: 0.020–0.050%, Ti: 0.0090–0.0160%, Nb: 0.060–0.100%, N: 0.0005–0.0050%, V: 0.08–0.25%; the remainder being Fe and other unavoidable impurities.

4. The hot-rolled strip steel for building structures according to any one of claims 1 to 3, wherein the base layer has a microstructure of ferrite + bainite + martensite, the bainite + martensite content is 5% to 15%, and the average grain size of ferrite is ≥ 8.

5.

5. The hot-rolled steel strip for building structures according to any one of claims 1 to 4, wherein the base layer has a yield strength of ≥ 460 MPa, a tensile strength of ≥ 580 MPa, a yield ratio of ≤ 0.81, and an impact energy of ≥ 190 J at -40°C.

6. The hot-rolled steel strip for building structures according to any one of claims 1 to 5, wherein the corrosion-resistant layer has a single equiaxed α-Ti microstructure.

7. Hot-rolled steel strip for building structures according to any one of claims 1 to 6, wherein the corrosion rate of the corrosion-resistant layer against sea wave spray is ≤ 0.006 mm / year.

8. The hot-rolled steel strip for building structures according to any one of claims 1 to 7, wherein the interface transition layer has a thickness of ≤ 8 μm, an average particle size of 15 to 40 μm, contains (Ti,Nb)C precipitated particles of < 120 nm, and has an interface shear strength of ≥ 268 MPa.

9. The hot-rolled steel strip for building structures according to any one of claims 1 to 8, wherein the thickness of the hot-rolled steel strip is 1 to 16 mm.

10. A hot-rolled steel strip for building structures according to any one of claims 1 to 9, wherein the base layer of the hot-rolled steel strip has a yield strength of ≥ 460 MPa, a tensile strength of ≥ 580 MPa, a yield ratio of ≤ 0.81, and an impact energy of ≥ 190 J at -40°C; the corrosion rate of the corrosion-resistant layer against ocean wave spray is ≤ 0.006 mm / year; and the interfacial shear strength is ≥ 268 MPa.

11. A method for manufacturing hot-rolled steel strip for building structures according to any one of claims 1 to 10, wherein the method is carried out in the following order: 1) Smelting and casting Based on the respective compositions of the base layer and corrosion-resistant layer described in any one of claims 1 to 3, the base layer and the corrosion-resistant layer are smelted and cast into a slab; 2) Assembly of the slab The surfaces of the slabs for the base layer and the corrosion-resistant layer are ground and polished, and peripheral welding sealing is performed along the contact surfaces of the slabs to form a clad slab including the base layer and the corrosion-resistant layer; after welding sealing, the bonding interface is subjected to vacuum treatment; 3) The clad slab is heated and rolled to form a steel strip, and within The clad slab is heated to 900-1000°C; Rough rolling is performed at a temperature of ≥860°C; finish rolling is performed at a temperature of 760-850°C, preferably 780-850°C; the pass reduction ratio is 5-20%, preferably 10-15%; and the cumulative reduction ratio is ≥88%. 4) Cooling The steel strip is cooled to a temperature of 300 to 450°C, and then wound up at this temperature to produce the hot-rolled steel strip. A method that includes a process.

12. The method according to claim 11, wherein in step 2) the thickness of the corrosion-resistant layer is 1 to 10% of the thickness of the clad slab; and / or in step 3) the thickness of the interface transition layer formed between the base layer and the corrosion-resistant layer is ≤ 8 μm.

13. The method according to claim 11 or 12, wherein in step 4) the cooling comprises two stages of cooling, in the first stage, after leaving the rolling mill stand, the steel strip is cooled to 700 to 750°C at a cooling rate of 2 to 10°C / s; and in the second stage, the steel strip is cooled to 300 to 450°C at a cooling rate of 30 to 50°C / second.

Images